Conventionally, screws are tightened using a robot in, for example, an automated assembly line of various devices. For example, Patent Document 1 discloses a nut runner system in which a nut runner main body attached to a wrist part of a robotic arm is capable of mechanically equipped with one of a plurality of bits.
In more detail, as illustrated in FIG. 10, a nut runner main body 100 of the nut runner system disclosed in Patent Document 1 includes a bit changer 110 to which one of a plurality of bits 160 held by a holder table 170 (see FIG. 11) is attached.
The bit changer 110 includes a hollow shaft 120, an inner slide member 130 disposed inside the hollow shaft 120, and an outside slide member 140 disposed outside the hollow shaft 120. A plurality of notches 121 are formed at suitable locations of the hollow shaft 120, and balls 150 are disposed inside the notches 121, respectively. Moreover, recesses 141 into which the balls 150 fit are formed in the outside slide member 140.
A recess 161 which opens radially outward is formed in an upper part of each bit 160. When the upper part of the bit 160 is inserted into the hollow shaft 120 of the bit changer 110, the inner slide member 130 is pushed by the bit 160 to move upwardly. Then, the balls 150 fit into the recess 161 and the outside slide member 140 moves downwardly. Therefore, the bit 160 is attached to the bit changer 110.
In order to remove the bit 160 from the bit changer 110, the outside slide member 140 is moved upwardly. Then, the balls 150 fit into the recesses 141 of the outside slide member 140, and the bit 160 is able to be slipped out from the hollow shaft 120. As illustrated in FIG. 11, a projection 171 is formed in the holder table 170 in order to move the outside slide member 140 upwardly.